We deployed D16714 and reran one of the failing tasks -- it completed cleanly as expected. Thanks!

Yep! It looks like that's the issue:

I'll give that a try. I think the associated diffs have enormous lines, so it seems likely that's what's going on.

(Following up for Greg, as I'm now the oncall.)

mysql> select @@max_allowed_packet;
+----------------------+
| @@max_allowed_packet |
+----------------------+
|             67108864 |
+----------------------+
1 row in set (0.00 sec)

metamta.differential.inline-patches is 500.
metamta.email-body-limit is still the default of 524288.

To bring this a bit back on topic, I think adding a Remarkup-rendered view that was not diff aware (as a first pass) would be very useful at pretty low implementation cost.

It looks like adding GFM or other markdown renderers has negative security implications, among other issues (see this discussion and T2849). We just want some sort of markdown renderer (i.e. remarkup) for checked-in files, which I think (without too much investigation) should be pretty straightforward to implement.